Anode for a discharge tube

ABSTRACT

An improved anode for a discharge tube is provided in which an anode member is positioned within an anode receiving envelope and wherein the anode is constructed of a thermal-expanding material such that during operation of the discharge tube the anode expands into intimate mechanical and thermal contact with the envelope.

United States Patent 1 1 1111 3,760,213 Buzzard 1 Sept. 18, 1973 ANODE FOR A DISCHARGE TUBE FOREIGN PATENTS OR APPLICATIONS 1 lhvenwri Robe" Bullardi Palo Alto, Calif- 964,265 7/1964 Great Britain 313 40 [73] Assignee: Coherent Radiation, Palo Alto, Calif.

. Primary ExaminerRonald L. Wibert [22] 1971 Assistant ExaminerPaul A. Sacher [21] Appl, No.: 138,815 Attorney-Limbach, Limbach & Sutton 52 US. Cl. 313/39, 313/46 ABSTRACT [51] f- 7/24! Holj 61/52 Holk H58 An improved anode for a discharge tube is provided in [58] Fleld of Search 313/36, 39, 40, 46 which an anode member is positioned within an anode receiving envelope and wherein the anode is con- [56] References C'ted structed of a thermal-expanding material such that dur- UNITED STATES PATENTS ing operation of the discharge tube the anode expands 2,829,271 4/1958 BOUChei 313/39 x into intimate mechanical and thermal Contact with the 3,227,905 1 1966 Talcott 313 39 envelope. 1,924,318 8/1933 Hull et al.... 3l3/46 X i 3,582,707 6 1971 Hynes 313/46 11 Claims, 6 Flglll'es I4 20 I4 20 l4 l2 l l l l 3 I2 54 32 38 22 24 20 i4 20 I4 Z0 8 A I l I/ k I g PATENTED SEPI 8l973 smurf;

INVENTOR.

ROBERT J. BUZZARD &

ATTORNEYS ON qr PATENTEBSEP1 8 I975 SHEU20F3 0 ZDZEEMC HlSNEH NI JSNVHD INVENTOR.

ROBERTJ. BUZZARD BY ATTORNEYS FIG.3

PATENTEUSEP18I973 3,760'21 3 sum 3 or 3 INVE'N TOR.

ROBERT J. BUZZARD ATTORNEYS ANODE FOR A DISCHARGE TUBE BACKGROUND OF THE'INVENTION The present invention relates to an improved anode and in particular to an improved anode for a discharge tube device, such as a gas ion laser.

In a power tube such as an ion laser discharge tube large amounts of current are passed through the anode. This causes large amounts of heat to be generated which must be dissipated. Anodes for a laser and other power tubes are mounted in an envelope or sleeve. In graphite core lasers, the circumference of the anode and envelope is sufficiently large that the heat developed by the anode could be radiated from the anode through the vacuum within the plasma tube and then dissipated through the envelope by means of a watercooled heat sink.

With the development of laser plasma tubes using beryllium (Be), the diameter of the discharge tube, and hence the envelope and anode, has been reduced. Consequently, the amount of surface exposed to the watercooled heat sink diminished. The lowered heat radiation rate proved to be insufficient and the anodes were found to melt and otherwise be damaged.

Thus, dissipating heat by radiation has not proven to be acceptable. One other way that the problem can be solved is by dissipating the heat from the anode by conduction. To accomplish this a thermal path must be provided from the anode to the anode-receiving sleeve where the heat is removed by heat transfer means.

There are presently several ways used in power and laser tubes for removing the heat from the anode by conduction:

l. The anode is enclosed in a metal envelope or cylinder and the anode is brazed to the envelope. The outer surface of the metal cylinder is in direct contact with a heat exchange system and hence the heat that is generated in the anode is conducted through the anode directly through the metal cylinder to the heat exchange system. 2. The anode is enclosed, for example, in a beryllium sleeve and an appendage is provided at one end of the anode which extends out of the beryllium sleeve and conducts heat from the anode. The appendage is then cooled. Unfortunately, this arrangement results in a fairly cumbersome and indirect means of removing the heat. 3. The anode is brazed directly 'to, for example, the beryllium sleeve in a Be0 discharge tube so that there is a direct conduction path to the cooling jacket surrounding the beryllium sleeve. This entails many difficult and expensive construction techniques.

SUMMARY OF THE INVENTION In accordance with the invention, an anode for a discharge tube such as a laser discharge tube, is made of a highly thermal expansive material such as copper. The anode is constructed such that when it is placed within the anode-receiving envelope or sleeve, which may be of a metallic or ceramic material such as Be0, and heated during the operation of the tube, the anode expands within the beryllium sleeve to form a close thermal and mechanical contact. Having such a close thermal contact with the beryllium sleeve, the heat generated by the anode is conducted directly from the anode through the anode-receiving sleeve and the heat removed by suitable heat transfer apparatus such as a water jacket surrounding the sleeve.

The anode of the present invention has the advantage over prior art devices l) and (3) above in that no brazing is required between the anode and the beryllium sleeve. Further, it has the advantage over (2) above in that no additional appendage is required remote from the anode/envelope combination. In addition to the requirement that the anode be made of a high thermal expansion material, in many application the anode material should also be ductile. F or example, a ductile material such as copper which also has good thermal expansion properties, should be used where the envelope or sleeve is a brittle material such as Be0. Ductility is required in order to prevent fracturing of the Be0 sleeve during the thermal expansion. Tungstun for example, would be a poor material because it is not ductile.

The sleeve, which may be made of beryllium or other ceramic, or which may be made of a metal, must be cooled adequately so that it does not expand relative to the anode. It also must be cooled in order to dissipate the heat generated by the anode.

In accordance with another feature of the invention, expansion means are provided in the anode allowing for axial thermal expansion of the anode during warmup of the tube. Additionally, axial stress relief grooves are provided in those portions of the anode which are in contact with the anode-receiving envelope. Without these axial stress relief grooves axial forces produced by uneven heating along the anode would tend to cause stresses in the anode.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates a discharge tube for a laser, partially in section, having an improved anode in accordance with the present invention.

FIG. 2A is an enlarged view of the improved anode of FIG. 1.

FIGS. 2B and 2C are views of the improved anode of FIG. 2A taken in the direction indicated by the arrows.

FIG. 3 illustrates the cooling apparatus used to cool the discharge tube of FIG. 1. a

FIG. 4 is a graphical diagram of the thermal expansion characteristics of materials used in the construction of an anode in accordance with the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A plasma discharge tube 10 for use in a laser utilizing the present invention is shown in FIG. 1. Additional details of the design and construction of a gas ion laser bore tube of this type is described in copending U.S. Pat. application Ser. No. 72,009, entitled Laser Bore Tube and Method of Making the Same, by Robert J. Buzzard and assigned to the assignee of the present invention. While the embodiment of the invention described herein is for use in a laser discharge tube constructed of Be0, it is to be understood that the present invention is applicable to other types of discharge tubes and to discharge tubes made of diflerent materials other then Be0. The discharge tube 10 includes a bore tube assembly 12 which comprises a plurality of individual cylindrical ceramic segments 14. Each of the segments includes a central arc discharge bore or path 16 and a plurality of gas return paths 18. The segments 14 are made from a ceramic such as beryllia or alumina. Each of the segments '14 are joined together at their respective end faces 20 by a suitable glass frit joining material of a type described in the patent application referred to above.

Secured within a ceramic sleeve or envelope 22 is an anode assembly 24. The anode assembly-24 is hollow to allow the passage of light therethrough. At the opposite end from the anode assembly is a cathode assembly 26 which includes a cathode such as a dispenser cathode 28. Leads 30 extend from the cathode 28 to a suitable cathode power supply.

Secured to the anode assembly 24 at one end, and the cathode assembly 26 at the other end of tube 10, are brewster window assemblies 32 which include sealed windows 34 located at brewsters angle to the axis of the core 12. In practice it has been found that the brewster window assembly 32 may be attached by a metallic bond 36 at the cathode end and at the anode end. Of course, to avoid corrosion problems due to galvanic action, the cooling jacket shown in FIG. 3, which surround the bore tube 12 should not extend as far as the bonds 36 and 38. Thus, the water within the cooling system which may be ordinary non-de-ionized water,

' will only come in contact with the segments 14 which are bonded to one another by the non-electrically conducting glass frit joints 20.

Details of the construction of the improved anode of the present invention are shown in FIGS. 2A through 2C. The anode 24 includes a hollow elongated cylindrical body 40. Light generated by the laser is transmitted through the anode through the hollow or bore portion 42 thereof.

The cylindrical body 40 is provided with a plurality of radially extending discs 44. These discs contact the anode receiving sleeve 22 and provide the conduction path from the interior of the anode 24 to the envelope 22 and to the heat exchange system.

As explained above, during operation of the discharge tube, the anode warms up and as it does it expands. Thus, the disc members 44 expand radially into intimate mechanical and thermal contact with the sleeve 22 of the discharge tube.

In addition to the radial expansion due to the heating of the anode, axial expansion occurs. In order to allow for axial expansion during the startup or warmup of the discharge tube, means are provided for permitting axial thermal expansion of the anode. In the embodiment of FIG. 2 an expansion member 46 is provided as a part of the anode tube 40. In the embodiment of FIG. 2 the expansion member 46 is formed by providing slots 48 along a portion 50 of the anode body 40. The slots 48 are provided in a radial direction and occur alternately every 180. Of course, it should be understood that other means may be provided for allowing actual expansion, the embodiment shown in FIG. 2 merely being illustrative.

As can best be seen by reference to FIGS. 2B and 2C the discs 44 are provided with a plurality of grooves 52. These grooves give the disc members 44 greater flexibliity so that during the startup of the discharge tube axial stresses resulting from axial expansion of the anode 24 is alleviated.

Referring to FIG. 3, discharge tube is enclosed within a magnet assembly 54 which includes a magnet cover 56. The magnet assembly provides a magnetic field along the length of the discharge tube 10 in order to confine the plasma to a small cross-sectional area. Located between the magnet assembly 54 and the discharge tube 10 is an annular passageway 58 through which a coolant is provided in order to remove heat generated within the discharge tube and the anode assembly 24. A suitable coolant such as water enters through an inlet tube 60 to a manifold 62. The coolant is then circulated through the anode assembly and the remainder of the discharge tube and leaves through an exit tube 64. Gas for use in the discharge tube is provided through a gas tube 68 to the discharge tube 10.

In the preferred embodiment of the invention, the anode 24 is constructed of a material having a greater thermal expansion rate than that for the anode receiving sleeve. In the embodiment described and illustrated herein, the anode was constructed of copper or of a copper/molybdenum alloy and the anode receiving sleeve 22, which forms a part of the bore tube, is constructed of beryllim (Be0). However, it should be noted that it is not absolutely essential that the anode material have a greater thermal expansion rate than the anode receiving envelope. This is because the anode receiving sleeve, being in direct contact with the coolant during the operation of the tube, will be maintained at a fairly constant temperature. Thus, the heat developed within the anode will eventually cause the temperature of the anode to rise to a sufficiently high degree that the resulting thermal expansion will cause the anode to come in contact with the envelope. The latter is true provided that the initial tolerances, i.e., the distance between the anode and the envelope, are not sufficiently great.

With a copper anode and with a beryllium sleeve, it has been found that an ideal tolerance, when the discharge tube is cool, between the anode and the sleeve is 1 mil (0.001 inch). However, good thennal and mechanical contact will result with a tolerance as great as 3 mils (0.003 inch).

In the embodiment illustrated the anode receiving sleeve formed one segment of the overall discharge bore tube. It should be understood however, that the envelope receiving sleeve may form a part of a single, continuous discharge tube in accordance with the present invention.

As can thus be seen by reference to FIG. 1 the anode 24 is initially slid in place within the envelope 22. The anode is mounted within the discharge tube 10 in a cantilever fashion by welding or otherwise securing, such as by the use of a glass frit material, the end portion 70 of the anode 24 to the discharge tube at 38.

While the embodiment described relates to an application for a laser discharge tube using a beryllium core, it should be understood that the invention in its broadest aspect is applicable to other types of laser discharge tubes and other types of power tubes. Furthermore, the specific materials described are illustrative of suitable materials for the particular application described and other materials performing similar functions can be substituted therefore.

I claim:

1. Anode for a discharge tube comprising:

a. an anode-receiving envelope forming a part of said discharge tube;

b. anode member;

c. means for positioning said anode member within said envelope; and

(I. wherein said anode is of an electrically conducting,

thermally-expanding material whereby said anode expands into intimate mechanical and thermal contact with said envelope during the operation of said discharge tube.

e. wherein said anode member comprises a longitudinally extending body and including means for permitting longitudinal expansion of said anode during startup of said discharge tube; and

f. wherein said anode includes a central bore tube and includes a plurality of discs extending radially therefrom for engaging said envelope.

2. Anode as in claim 1 wherein said expansion means comprises an expansion joint.

3. Anode as in claim 1 wherein said anode member comprises a generally hollow, cylindrical body, and said envelope includes a correspondingly shaped receiving portion.

4. Anode as in claim 3 wherein said expansion means comprises an expansion member forming an integral part of said anode member.

5. Anode as in claim 3 wherein said discs include means for relieving axial stresses resulting from axial expansion of said anode during discharge tube stanup.

6. Anode as in claim 1 wherein said anode member is made of copper.

7. Anode as in claim 3 wherein said anode member is made of copper.

8. Anode as in claim 1 wherein said envelope is constructed of Be0.

9. Anode as in claim 3 wherein said envelope is constructed of Be0.

l0. Anode as in claim 1 wherein said anode member is made of a ductile material.

11. Anode as in claim 3 wherein said anode member is made of a ductile material.

' l It t 

1. Anode for a discharge tube comprising: a. an anode-receiving envelope forming a part of said discharge tube; b. anode member; c. means for positioning said anode member within said envelope; and d. wherein said anode is of an electrically conducting, thermally-expanding material whereby said anode expands into intimate mechanical and thermal contact with said envelope during the operation of said discharge tube. e. wherein said anode member comprises a longitudinally extending body and including means for permitting longitudinal expansion of said anode during startup of said discharge tube; and f. wherein said anode includes a central bore tube and includes a plurality of discs extending radially therefrom for engaging said envelope.
 2. Anode as in claim 1 wherein said expansion means comprises an expansion joint.
 3. Anode as in claim 1 wherein said anode member comprises a generally hollow, cylindrical body, and said envelope includes a correspondingly shaped receiving portion.
 4. Anode as in claim 3 wherein said expansion means comprises an expansion member forming an integral part of said anode member.
 5. Anode as in claim 3 wherein said discs include means for relieving axial stresses resulting from axial expansion of said anode during discharge tube startup.
 6. Anode as in claim 1 wherein said anode member is made of copper.
 7. Anode as in claim 3 wherein said anode member is made of copper.
 8. Anode as in claim 1 wherein said envelope is constructed of Be0.
 9. Anode as in claim 3 wherein said envelope is constructed of Be0.
 10. Anode as in claim 1 wherein said anode member is made of a ductile material.
 11. Anode as in claim 3 wherein said anode member is made of a ductile material. 